Drying machines



Jan. 21, 1969 R. J. ARCHER 3,422,882

DRYING MACHINES Filed Oct. 15, 1966 Sheet of 5 vFIG/1.

.1m. 21, 1969 R. J. ARCHER 3,422,882

DRYING MACHINES Filed Oct. 13. 1966 Sheet 2 of 5 f E53 O (D I: 6 L P r (\1 99 g @R F \fl R-- k1 DE- k Q F r R. J. ARCHER DRYING MACHINES Jan. 21, 1969 Sheet Filed Oct. 13, 1966 wow 0601 MVOE Qmm United States Patent 44,650/ 65 US. Cl. 165-1 10 Claims Int. Cl. F26b 3/20, 9/00; G05d 23/19 ABSTRACT OF THE DISCLOSURE The disclosure is concerned with a method for heating a platen in a drying machine in which the selected drying temperature in a platen heating chamber is accurately maintained and the latent heat of steam is utilized by establishing and maintaining a reduced pressure condition in the heating chamber such that the boiling point of Water is reduced to the required drying temperature. A heating arrangement for a drying machine is also disclosed. The heating arrangement includes a platen heating chamber, steam supply and suction means. Control means are disclosed for maintaining the pressure and temperature conditions required. The control means may be operative automatically from members which sense the pressure or temperature of the heating chamber.

This invention relates to drying machines and more particularly to platen heating arrangements therefor and to a method of heating a platen of a drying machine. The invention is particularly applicable to leather drying machines but may well be employed for other purposes.

A leather drying machine basically comprises a platen surface on which the skin to be dried is spread or slicked, means for heating the platen surface to provide drying heat and means to evacuate the space above the platen to assist the extraction of moisture from the skin by facilitating boiling at temperatures below 100 C. thus avoiding damage to the leather and to remove the moisture thus extracted.

Platen structures have in the past been mainly heated by water. This has been due to the necessity of ensuring that the platen surface never rises beyond a certain temperature, which varies with the type of skin being dried. If an excess temperature were achieved, it would have a damaging effect on the skin. Thus in order to ensure that the required temperature is never exceeded, the supply of water has had a carefully controlled temperature which has normally been the maxim permissible temperature.

These platen structures have been constructed'of mild steel having a chromium plated working surface, provision being made under the surface for the circulation of heated water. The platen surface in these cases was of the order of a quarter of an inch in thickness or in some cases considerably thicker. Thus a considerable amount of the heat in the water has been used to heat the platen before it has been possible to provide heat for the skin. Thus long warming and cooling down periods have been necessary and heat transfer to the skin has been slow.

The present invention seeks to obviate or substantially reduce these disadvantages by providing heating which will provide considerably greater amounts of heat than that provided by the water while still permitting accurate control of the temperature.

Still greater efficiency may be achieved by replacing standard platen structures with those described in our copending application No. 44,652/ 65. The overall combination of the present invention with the platen structure of our co-pending application No. 44,652/65 and the skin handling arrangement of our co-pending application No. 44,651/ 65 will provide a leather drying machine of exceptional efficiency as compared to most existing machines.

Patented Jan. 21, 1969 According to the invention a heating arrangement for a drying machine comprises a supply of steam and a suction means both connected to the heating chamber of a platen and control means whereby the pressure in the heating chamber is such that the boiling point of water is reduced to the required drying temperature, thus making available the latent heat of the steam for drying purposes while accurately controlling the temperature produced.

Further according to the invention there is provided a method of heating a platen for a drying machine comprising supplying steam to the platen heating chamber, removing fluid from the platen heating chamber by suction and controlling the steam supply and the suction such that the boiling point of Water is reduced to the required drying temperature as a result of the pressure in the platen heating chamber, thus making available the latent heat of the steam for drying purposes while accurately controlling the temperature produced.

Preferably the operation of the control means is automatic whereby once the temperature of the platen is set, the control means will ensure correct pressure of steam in the platen;

One embodiment of the invention will now be described by Way of example with reference to the accompanying drawings in which:

FIGURE 1 is a side view of a leather drying machine having a heating arrangement in accordance with the invention;

FIGURE 2 is a view of the controls of a leather drying machine of FIGURE 1; and

FIGURE 3 is a schematic diagram showing the control for one of a stack of platens and its associated vacuum hood.

Referring to FIGURE 1 a leather drying machine consists basically of a platen assembly 1, transfer arrangements 2 and control gear 3. The present application relates mainly to the control gear and platen structure where it affects the heating of the platen, the platen itself being described in our co-pending application No. 44,651/ 65 and the transfer arrangements being described in our co-pending application No. 44,652/ 65.

Thus the description of the machine will only be described in relation to platen heating. The leather drying machine shown has a stack of six platen structures 4, 5, 6, 7, 8 and 9 containing five platen surfaces 10, 11, 12, 13 and 14 consisting of stainless steel sheets. Each of the platen structures 5, 6, 7 and 8 have a vacuum hood on the underside and a platen surface heating arrangement in their upper part. The platen structure 4 has only a platen surface heating arrangement and the platen structure 9 has only a vacuum hood.

The platen surface 14 is shown separately from the platen structures 8 and 9 between which in normal operation it is sandwiched, the machine being at the point at which the platen surface 14 is about to be removed.

A main control unit 15 is provided for controlling the supply of steam and the evacuation of the plates; the operation of this control unit will be described hereafter with reference to FIGURE 3.

As can be seen from FIGURE 2, the control unit 15 has five sets of controls, one for each platen. Thus each platen has its associated automation control unit having a meter 16 with two needles, 17 for setting the desired temperature (operable by means of a knob 18) and 19 which reads the actual temperature achieved. Two auxiliary meters 20 and 21 provide readings of input and output air pressures to and from the automatic control unit. Below the automatic control unit is a settable pressure switch 22 which controls the platen vacuum at which steam is first injected to ensure a suitably small proportion of air is mixed with the steam.

The control unit is connected to the platens by a plurality of pipes and valves (not shown) which will hereinafter be referred to with reference to FIGURE 3.

The electrical supply and general controls are housed in a separate cabinet 30. The main on-off switch is shown at 31 and time controls for each platen are shown at 32. A switch 33 is provided for isolation of the electrical supply in conjunction with a door lock and the switches 34 to 37 respectively control vacuum pump on/otf, manual platen raising control, manual automatic selection, andmanual platen lowering control.

A panel 39 in the main control unit houses relays.

Referring now to FIGURE 3 the control arrangements will now be described together with their operation. FIG- URE 3 shows diagrammatically the parts of the control arrangement and their interconnections. Details are only shown of the control of one platen and its associated hood, all other platens being controlled in the same way.

In this diagram 101 represents the vacuum pipe and 102 the steam pipe. An air pressure supply is shown at 103. The vacuum pipe is connected to the platen 104 by way of a pneumatically operated valve 105 and to the vacuum hood 106 by way of a pneumatically controlled valve 107. The pneumatically controlled valves 105 and 107 are in turn controlled by electrically operated air valves 108 and 109 respectively, the valve 108 being controlled by a relay RA/2 by way of contact RA1 and the valve 109 being controlled directly by a timer 110 which controls the sequence of operations of the platen and the vacuum hood. As can be seen, the timer is also connected to the relay RA/ 2 and to a second relay RB/4.

The valve 105 is by-passed by a pipe 111 in which are positioned an orifice 112 and an electrically operated valve 113 controlled by relay RB/4 by way of contact RB4.

Steam is admitted to the platen by a pneumatically operated valve 114. Valve 114- is controlled by an electrically operated air valve 115. Electrically operated dump valves 116 and 117 are provided for the platen and hood respectively. These valves connect the platen and hood to atmosphere at the end of a cycle and are controlled by both relays RA/2 and RB/4 by contacts RBI and RAZ in series. An air control unit 118 supplies air to the valve 114 in response to its setting. This unit 118 is one of the units indicated on the main control unit 15 by references 16 to 21 (FIGURE 2). Temperature sensing for the unit 118 is achieved by a senser element 119.

Two pressure sensitive switches 120 and 121 are provided controlling respectively the valve 115 through contact RB4 and the relay RB/4 by by-passing its holding contact RB2. The switch 121 is one of the switches 22 in the control unit 15 (FlGUREQ). The relay RA/2 is also controlled by the relay RA/4 through contact RB3.

The operation of the control arrangement will now be described for one cycle of operation:

This cycle starts when the hood is engaged with the platen. The operating temperature and initial pressures are assumed to have been set and the hood and platen are open to vacuum.

The timer 110 provides a signal to relays RA/2 and Rl3/4 and to valve 109. RA/2 is energised and reverses its contacts RA1 and RA2. RB/4 is not energised since contact RB2 is open and pressure switch 121 is open as a result of atmospheric pressure in the platen. Valve 109 opens to admit air to valve 107 which also opens to connect the hood 106 to vacuum. RA1 closes to open valve 108 and admit air to valve 105. Valve 105 then opens to connect the platen 104 to vacuum. RA2 opens to close dump valves 116 and 117.

Thus the platen and the hood are pumped down until a predetermined vacuum is reached as sensed by the pressure switch 121. This switch closes to bypass open contact RB2 and energise relay RB/4 charging over all its contacts. RBI opens but provides no action at present since RA2 is already open. It does, however, hold the dump valves 116 and 117 closed when relay RA/Z is deenergised as will be seen. RB2 closes and holds relay RB/4 energised irrespective of the pressure switch 121. R83 opens to deenergise relay RA/Z. RB4 closes and opens bypass valve 113 and allows the steam valve 114 to be controlled, by way of valve 115, by the pressure switch 120. Additional control of the valve 114 is also provided by the control unit 118 which controls the air supply to valve 114 in accordance with its setting and the temperature sensed by sensor 119. Because RA/2 is deenergised RA1 opens to deenergise the valve 108 and close the valve shutting off the main connection of the platen 104 with the vacuum. This is, of course, by-passed by the orifice 112 (which controls the vacuum connection and the valve 113 which is open). RAZ closes but has no efiect in view of the opening of RB1.

The time signal then continues for the set drying time, the steam supply for drying being controlled during this period by the control unit 118 and the pressure switch 120. At the end of the set period the time signal is cut off. This deenergises the relay RB/4 and the valve 109. RBI closes to open the dump valves 116 and 117 to atmosphere to allow parting of the hood and platen. RB2 opens to return holding circuit for the next operation. RB3 closes to allow RA/ 2 to be reenergised on the next cycle. RB4 opens to close the steam valve 114 and the by-pass valve 113. Valve 109 closes to shut off valve 107 isolating the vacuum from the hood.

The control apparatus is thus reset for the next cycle and the dried skin can be replaced by another wet skin.

It will be appreciated that while the above description relates to a leather drying machine, it could equally well be applied to other drying and/or heating machines requiring equally accurate control, where the desired heating temperature is in the appropriate range.

1 claim:

1. A heating arrangement for a drying machine comprising a platen heating chamber, a supply of steam coupled to said heating chamber via a first valve, a suction means coupled to said heating chamber, and control means coupled to said first valve for maintaining the pressure in said heating chamber such that the boiling point of water is reduced to the required drying temperature whereby the latent heat of steam at the required drying temperature is made available for drying and the temperature is accurately controlled.

2. A heating arrangement for a drying machine according to claim 1 including a second valve connected between said suction means and said heating chamber and wherein said control means is coupled to said second valve.

3. A heating arrangement for a drying machine according to claim 1, wherein said control means includes a means for sensing the pressure in said heating chamber whereby the pressure is automatically controlled.

4. A heating arrangement for a drying machine according to claim 2, wherein said control means includes a means for sensing the pressure in said heating chamber whereby the pressure is automatically controlled.

5. A heating arrangement for a drying machine according to claim 1, wherein said control means includes means for sensing the temperature of said heating chamber.

6. A heating arrangement for a drying machine according to claim 2, wherein said second valve remains open during drying time and a reduced orifice is positioned between said second valve and said heating chamber.

7. A heating arrangement for a drying machine according to claim 6, including a third valve which is pressure sensitive connected in parallel with said second valve and said reduced orifice between said suction means and said heating chamber for initially reducing the pressure in said heating chamber, said third valve being closed during drying time.

8. A heating arrangement for a drying machine according to claim 1, wherein a dump valve is connected between said heating chamber and a point of atmospheric pressure.

9. A heating arrangement for a drying machine according to claim 2, including a timing means controllably coupled to said first valve, said second valve and a dump valve which connects said heating chamber to a point of atmospheric pressure for closing said first valve and said second valve and opening said dump valve after a predetermined drying time.

10. A method of heating a platen of a drying machine comprising reducing the pressure in a platen heating chamber to that pressure at which water will boil at the required drying temperature, supplying steam to said platen heating chamber, removing fluid from said heating chamber by suction, and maintaining the pressure in said heating chamber by controlling the amount of steam supplied and the amount of suction whereby the latent heat of the steam 15 at the required temperature is made available for drying purposes and the temperature in the heating chamber is accurately controlled.

References Cited UNITED STATES PATENTS 3,316,655 5/1967 Bocciardo 3492 ROBERT A. OLEARY, Primary Examiner.

10 C. SUKALO, Assistant Examiner.

US. Cl. X.R. 

